On the Polarity of SSC and SI Observed in Low Latitudes
Tsunomura, S.
Abstract
Statistical and numerical analyses are made for polarity of SSC and SI observed at Japanese chain magnetic observatories, Memambetsu, Kakioka, Kanoya and Chichijima. Statistics for polarity of SSC and SI observed at Kakioka are taken on the basis of the reports of rapid variations from 1957 to 1992. It is shown that the polarity of D component is positive (eastward) in most cases as well as H and Z components (northward for H and vertically downward for Z). In the statistics taken on the basis of magnetic data converted to the geomagnetic dipole coordinate system, there is not a definite shift in polarity of D component for both of SSC and SI. But the correlation coefficients among Memambetsu, Kakioka and Kanoya do not always become larger by the conversion. Comparing the results of superposed epoch analysis of magnetic data with those of a numerical calculation, it is concluded that local time dependence of D component polarity is explained by a model of ionospheric current system driven by field-aligned currents as a source in high latitudes. Furthermore, it is suggested that the latitudinal variation in the magnetic field variation can be explained by superposition of the effects of the magnetopause current, field-aligned currents and the magnetotail current on the ionospheric current contribution. It is shown that the magnetic field variations of SSC and SI in horizontal components are apparently enhanced by ground induction effects at Memambetsu and Kanoya, and that those at Chichijima are not so much enhanced as expected. The characteristics of ground induction, especially at Chichijima, remain as problems to be clarified in future.
